The studies will will be concerned with the renal and intestinal excretions of fluoride and the retention of fluoride in patients with chronic renal disease in whom the major pathway of fluoride excretion, the kidney, is impaired. The fluoride intake will be derived from natural sources, such as the diet and fluoridated drinking water. These studies will be carried out under strictly controlled dietary conditions during a normal calcium intake and during a high calcium intake. The effect of aluminum, given as aluminum hydroxide which is used as a medication to decrease the elevated serum phosphorus level in chronic renal disease, will be investigated on the metabolism of fluoride. The effects of this antacid on fluoride metabolism will also be studied in patients with normal kidney function. Studies will also be carried out under conditions of a high fluoride intake on the effect of aluminum hydroxide on fluoride metabolism in patients with osteoporosis who are free of kidney disease and who receive sodium fluoride as a treatment for this bone condition. These patients will receive the aluminum-containing antacids as they have been and are still used to alleviate gastric irritation caused by large doses of fluoride. BIBLIOGRAPHIC REFERENCES: Spencer, H., Wiatrowski, E., Osis, D., and Norris, C. Effect of magnesium on the fluoride balance in man. IADR Supply. J. Dental Res., 55:194, 1976. Osis, D., Spencer, H., Wiatrowski, E., Coffey, J., and Norris C. Effect of fluoride and inorganic elements on serum magnesium in man. IADR Suppl. J. Dental Res., 55:194 1976.